1.1. Field of the Invention
The present invention relates to the field of electronic database management, and in particular to a method for increasing the performance of said database.
1.2. Description and Disadvantages of Prior Art
Electronic database systems store data information usually in a plurality of memories sections which are located in physical storage subsequent to each other. For example, in IBM relational and database technology those sections are so called “pages”, where in a page usually contains 0 or more table rows. On a logic level, several rows build up a table and several tables build up the table space which is managed as a set of single large binary files or a subdirectory structure respectively.
During usage of the database read, write and delete processes are directed to particular fields of a row. A modification of data may cause a non-optimal physical storage image, because for example a deletion of some rows may cause fragmentation problems. Further, for example if a field of a row is updated with a longer text string then originally present, a “over flow record” might be generated, where within the data field a pointer to a new storage location which preserves sufficient storage space, is stored. In such cases a subsequent read operation on the original data field is redirected to the larger data field which results in two separate I/O operations, instead of originally only one I/O operation. So, exhaustive usage of a database may result in a quite fragmented storage image. The more fragmented the storage image is, the higher is the number of redirections. As a consequence, average access times for read and/or write operations are increased relative to an “ideal” state.
Recommendations can be made to reorganize objects in the database, in order to reduce the fragmentation of the storage image. An instructive prior art publication, namely “Database Fragmentation and Disorganization” by Graig S. Mullins published as a DBA Corner column in the Database Trends and Applications magazine in December 2001, may be retrieved from: http://www.craigsmullins.com/dba-corner.htm.
It should be stressed that database reorganization procedures are considered to imply relatively high cost due to required system resources and because in some cases they are performed by professional database management staff.
Most prior art reorganization tools require that the object being reorganized has some period of time of unavailability to the applications. Some prior art reorganizations do even require the object to be unavailable during the entire reorganization process.
As an example of prior art, and with reference to FIG. 1, IBM's existing relational database technology DB2 provides two ways to support the user in decisions about doing the table and index reorganizations. There is the table and index reorganization check procedure CLP utility, i.e. an auxiliary services tool 14 that recommends reorganizations of certain tables and indexes, stored in the database 12. And in addition, DB2 provides the automatic table reorganization feature in a separate tool (not depicted in order to improve clarity) that is even capable of executing the table and index reorganization.
Both tools are based on plain table and index statistical information, i.e., meta data tables, like IBM DB2 CATALOG, which describe the logical and physical structure and properties of the database. This statistical information is not necessarily current because it is only collected on a periodic basis. They use certain formulas to analyze the statistics for indicators that table and index reorganization could be beneficial.
Disadvantageously, a prior art reorganization checking tool 14 is not able to predict that a recommended reorganization will actually have a positive impact on the database performance.